1. Field of the Invention
This invention relates to a solid electrolytic capacitor comprising a substrate and a capacitor element and, in particular, relates to a solid electrolytic capacitor packaged with a resin.
2. Description of the Related Art
Many solid electrolytic capacitors have a structure in which a solid electrolytic capacitor element is covered with a packaging resin and an anode and a cathode of the capacitor element are electrically connected to an anode terminal and a cathode terminal, respectively, provided outside the packaging resin. The packaging resin serves to maintain airtightness of the inside of the element and to electrically and mechanically protect the element itself.
As one example of such a capacitor structure, there is one in which a capacitor element is mounted on a substrate and covered with a packaging resin and an anode terminal and a cathode terminal are provided on the back side of the substrate to serve as mounting terminals. Japanese Unexamined Patent Application Publication (JP-A) No. 2006-93343 (Patent Document 1), for example, discloses this type of solid electrolytic capacitor. In Patent Document 1, a laminate of capacitor elements is used. This solid electrolytic capacitor is fabricated in the following manner. A dielectric oxide film layer is formed at the surfaces of each of valve metal bases and a solid electrolyte layer and a conductor layer are laminated on the surfaces of a region, excluding a capacitor element anode portion, of each valve metal base formed with the dielectric oxide film layer. The laminated solid electrolyte layer and conductor layer serve as a capacitor element cathode portion. Thereafter, in the state where the capacitor element anode portions are aligned together, the capacitor element cathode portions are bonded together using a conductive adhesive, so that a capacitor element laminate is formed. Then, a capacitor element laminate anode portion is bonded to the surface of an anode pattern of a substrate, being a member to be connected, by, for example, YAG laser welding, while, a capacitor element laminate cathode portion is bonded to the surface of a cathode pattern of the substrate by a conductive adhesive. Thereafter, the laminate fixed to the substrate at its predetermined regions in the manner described above is overmolded with an epoxy resin by casting using a vacuum printing method. In the state where a mold surface of the thus overmolded substrate faces upward, dicing is performed at intervals of, for example, 7.3 mm×4.3 mm on the basis of predetermined marking positions. Then, aging treatment is carried out by applying a constant voltage to a solid electrolytic capacitor according to a known method to sufficiently reduce leakage current (referred to as LC), thereby completing the fabrication.
As another example of such a solid electrolytic capacitor having the structure in which a solid electrolytic capacitor element is covered with a packaging resin and an anode and a cathode of the capacitor element are electrically connected to an anode terminal and a cathode terminal, respectively, provided outside the packaging resin, there is a resin-packaged chip-type solid electrolytic capacitor. Japanese Unexamined Patent Application Publication (JP-A) No. 2001-57321 (Patent Document 2), for example, discloses this type of structure. This chip-type solid electrolytic capacitor is fabricated in the following manner. At first, a compact, having a rectangular parallelepiped shape or the like, of metal tantalum powder embedded with a tantalum wire to serve as an anode lead is sintered, thereby producing a porous anode body. Then, a dielectric oxide film layer is formed by anodic oxidation on the surfaces of the anode body other than the anode lead portion. A solid electrolyte layer and a conductor layer are laminated on the surfaces of the dielectric oxide film layer, thereby obtaining a capacitor element. Then, a flat plate-shaped anode terminal with a portion extending straight out of a packaging resin body (to be formed later) is connected to the anode lead by electric resistance welding, laser welding, or the like. Further, a flat plate-shaped cathode terminal with a portion extending straight out of the packaging resin body (to be formed later) is connected to the cathode conductor layer at the surface of the capacitor element by a conductive adhesive. Further, the anode terminal or the cathode terminal, or both the anode terminal and the cathode terminal are immersed in a mixture of a solvent and polytetrafluoroethylene, then drying is carried out to volatilize the solvent, thereby forming a porous fluororesin body. Thereafter, the packaging resin body covering a predetermined portion is formed by transfer molding using a thermosetting resin such as an epoxy resin. Finally, the portions, extending out of the packaging resin body, of the anode and cathode external terminals are each bent along a side surface of the packaging resin body and further bent along a bottom surface thereof, thereby completing the fabrication.